1. Field of the Invention
The present invention relates to PWM power regulators and/or multi-phase DC-DC converters, and more particularly to a clockless, cascading, current-mode regulator with high noise immunity and arbitrary phase count.
2. Description of the Related Art
Multi-phase power conversion and current-mode control are commonly used methods for DC-DC power conversion for the electronic market. Multi-phase power conversion provides a cost-effective power solution when load currents are no longer easily supported by single-phase converters. The switching of each channel is timed to be symmetrically out of phase with each of the other channels. The multi-phase approach offers cost-saving advantages with improved response time, superior ripple cancellation, and improved thermal distribution.
The electronic market has evolved, however, to the point that the number of phases required in a multi-phase power regulator exceeds the number that a single integrated circuit (IC) can practically support. As the phase count grows above four, the IC package becomes large, and the spacing between the power-delivery point and the controller IC exceeds the distance that can accurately support low-level signal integrity and noise rejection. Signal problems necessitate added expense in terms of extra components to suppress noise, layout constraints, and reduced phase count.
Prior methods attempt to solve the excessive package size problem (which is only part of the overall problem) by cascading multiple current-mode regulators. In one case, a separate controller IC generates a triangle-shaped signal common to all of the current-mode regulators. Each of the current-mode regulators initiates its cycle at a different, programmable point on the triangle-shaped signal in an attempt to achieve the necessary phase separation between the different channels. Correct phase separation between the different channels is an important component to multi-phase power conversion necessary for ripple cancellation.
Other problems remain unsolved by prior solutions. The triangle-shaped signal is an analog signal, and is therefore subject to signal degradation and noise interference. Thus the prior method is constrained in terms of the physical separation of the different channels. The noise generated by one channel switching corrupts the triangle-shaped signal reaching the other channels, which limits the time separation between two channels to some value necessary to allow the noise to dissipate. Since the time separation between the channels is limited, so is the phase count and/or switching frequency.